1. Field of the Invention
The present invention relates to a data symbol reader which reads coded data, such as a two-dimensional data symbol.
2. Description of the Related Art
For instance, in a POS system, a bar code which represents sales information of merchandise is read by a bar code reader. However, the bar code is scanned with a scanning beam only in one direction (one-dimensional), i.e., the direction of the alignment of the bars which form the bar code. Consequently, the amount of data that can be recorded is limited.
To increase the amount of data to be transmitted, a data symbol reader which reads a two-dimensional data symbol consisting of a mosaic pattern of white and black areas having a matrix arrangement has recently been proposed. There are primarily two types of data symbol readers, i.e., in one type the data symbol pattern is read at one time in two orthogonal directions by an area sensor such as a CCD, and in another type each line of the data symbol pattern is scanned by a line sensor in the main scanning direction. In the latter type, the data symbol and the reading portion are relatively moved in the sub-scanning direction perpendicular to the main scanning direction to read the two-dimensional pattern.
In particular, the first type using an area sensor has advantages over the second type, since no relative displacement between the data symbol and the reading portion in the sub-scanning direction is necessary in the first type.
FIG. 10 shows an example of a known data symbol reader that uses an area sensor. In FIG. 10, a data symbol reader 100 is comprised of a body 101 which includes a data symbol reading device 102, and a housing 103 formed integral with the body 101, which defines therein an enclosed interior space between the reading device 102 and a symbol reading area. The housing 103 is provided on the front end thereof with a rectangular opening which contains therein the symbol reading device 102.
Upon reading a data symbol, the data symbol and the data symbol reader are relatively moved so that the data symbol is located within the front opening of the housing 103.
In the arrangement shown in FIG. 10, a precise positioning of the data symbol relative to the symbol reader is necessary to align the data symbol with the opening of the housing 103 so that the entire data symbol is located within the front opening area of the housing. For example, if a part of the data symbol overlaps the front edge 104 of the housing 103 which defines the front opening, a reading error occurs.
In general, since the housing 103 is made of an opaque material for intercepting light, it is difficult for an operator to visually confirm the relative position of the data symbol to the front opening of the housing. In particular, even if the operator visually confirms that the data symbol is located within the outer edge 105 of the front end of the housing 103, there is still a possibility that the data symbol partly overlaps the inner edge 104 of the front opening of the housing, thus resulting in a reading error.
Under these circumstances, it takes long time to precisely position the data symbol within the front opening of the housing 103 and therefore negates the above-mentioned advantage of the data symbol reader having an area sensor.